Contents

Crytography is the science of secure communication in the presence of third parties (sometimes called "adversaries").

Modern cryptographers and cryptanalysts work in many areas including

data confidentiality

data integrity

authentication

forward secrecy

end-to-end auditable voting systems

digital currency

Classical cryptography focused on "data confidentiality" -- keeping pieces of informationsecret, i.e. of designing technical systems such that an observer can infer as few as possible - optimally none - information from observing the system. The motivation for this is that the owner of the system wants to prevent the observer from taking advantage (e.g. monetary, influential, emotional) of the possible intelligence.

This secrecy or hiding is achieved by removing contextual information from the system's observable state and/or behaviour, without which the observer cannot gain intelligence about the system.

It may be advantageous for an ATM machine to hide the information as to how much cash is still available in the machine. It may e.g. only disclose the information that no more bank notes are available from it to the holder of a valid debit card.

Well known entities with well known fields of activity may wish to hide the fact that they are communicating at all since an observer aware of their fields of activity may already from the fact of some communication happening, be able to infer information.